Synchronization of timing advance and deviation

ABSTRACT

A system and method for reducing the latency from timing deviation (TD) measurement to time advance (TA) adjustment. The invention uses a deterministic procedure to coordinate time advance (TA) commands and timing deviation (TD) measurements so that failed transmissions or mobile terminals signal propagation changes can be recognized and corrected much more rapidly. Radio resource efficiency is maximized by minimizing signaling overhead through effectively reducing the frequency of time advance commands. This is accomplished by using TA command signals which include a Connect Frame Number (CFN) to specify particular radio frames for time advance (TA) adjustment. The potential for timing deviation (TD) measurements to be incorrectly processed in conjunction with adjusting a physical reception window and calculating mobile termination location is minimized, without excessive command signaling requirements.

[0001] This application claims priority from U.S. ProvisionalApplication No. 60/195,087 filed Apr. 6, 2000.

[0002] The present invention relates generally to digital communicationsystems. More specifically, the invention relates to a system and methodfor synchronizing uplink and downlink transmissions for time divisionduplex and time division multiple access protocols to compensate forradio propagation delays. As an additional benefit, the systemsfacilitate geographic location of mobile terminals.

BACKGROUND

[0003] In the proposed 3^(rd) generation (3G) wireless protocols, timedivision duplex (TDD) and time division multiple access (TDMA) methodsdivide an allocated radio spectrum into repetitive time periods known asradio frames which are uniquely identified by a sequential cell framenumber (FN). Each radio frame is further subdivided into a plurality ofunique, numbered time slots (TS) which are individually assigned foruplink (UL) or downlink (DL) transmission.

[0004] Radio transmissions incur a propagation delay relative to thedistance from a transmitter to a receiver. In mobile cellularcommunication systems, these delays vary over time as the distancebetween a mobile terminal (MT) and a base station (BS) changes. In orderto receive communication transmissions without error, the time ofreception must be known to the receiver.

[0005] To compensate for varying propagation delays and to maintain aknown time of reception, the time of transmission is periodicallyadjusted. The transmission timing adjustment is performed in the MTrather than the BS since many MT's are supported by a common BS and thepropagation delay for each MT is different depending upon distance. TheBS downlink radio frame transmissions do not vary over time and are usedby an MT to synchronize uplink radio frame transmissions.

[0006] The MT synchronizes to a BS downlink transmission that hasincurred a propagation delay. The MT uplink transmission also incurs apropagation delay approximately equal to the downlink propagation delay.The uplink transmission received in the BS is the sum of the downlinkand uplink propagation delays. Radio frame reception (DL) and replytransmission (UL) at a MT before any timing adjustment is performed isshown in FIG. 1a. FIG. 1a illustrates a BS transmitted DL time slot (TS)received by the MT immediately followed by a MT transmitted UL time slot(TS). Radio frame transmission (DL) and reception (UL) at a base stationbefore any timing adjustment is performed is shown in FIG. 1b . FIG. 1billustrates one MT transmitted UL time slot immediately followed by a BStransmitted DL time slot.

[0007] As reflected in FIG. 1a, the MT synchronizes on the downlink timeslot reception at a time T1 and initiates its uplink transmissionimmediately thereafter. As shown in FIG. 1b , the start of the downlinktime slot (TS) transmission by the BS occurs at time T2 and the end of apreceding uplink time slot (TS) received by the BS occurs at time T3.The difference between times T3 and T2 is referred to as timingdeviation (TD) and is equal to the sum of the uplink and downlinkpropagation delays.

[0008] The TD can be identified and used to command the MT to adjust theuplink time slot transmission time in order to synchronize uplinktransmission with downlink reception at the BS. Since the MT issynchronized to a received downlink time slot that has already incurreda downlink propagation delay, the MT must advance transmission of uplinktime slots by the TD sum of uplink and downlink propagation delays. Thisis referred to as timing advance (TA) defined as:

T3−T2=TD=UL propagation delay+DL propagation delay=TA  Equation 1

[0009] Radio frame reception (DL) and reply transmission at an MT afterthe TA adjustment is shown in FIG. 2a. FIG. 2a shows a BS transmitted DLtime slot followed by a time advanced MT transmitted UL time slot at theMT. Radio frame transmission (DL) and reception (UL) at the base stationafter TA adjustment of the transmission is shown in FIG. 2b. FIG. 2bshows one BS transmitted DL time slot immediately followed by a timeadvanced MT transmitted UL time slot as received at the BS.

[0010] The MT has advanced the UL time slot transmission according tothe TA command from time T5 to time T4. Since the received time slot attime T5 has already incurred the DL propagation delay, the new MT timeslot transmission time T4 synchronizes the reception time T6 of the BSreceived UL time slot advanced by the expected UL propagation delay.

T4=T5−TA (sum of UL and DL propagation delays)  Equation 2

T5=T6 (BS next time slot)+DL propagation delay  Equation 3

T4=T6 (BS next time slot)−UL propagation delay  Equation 4

[0011] Accordingly, the TA adjustment of the MT transmissions results insynchronization of UL and DL time slots at the BS.

[0012] A BS controller is responsible for instructing the MT to adjustthe uplink transmission according to the calculated TA. MT commands forTA adjustment generated by the BS controller may require considerablephysical resources, it is important for the BS controller to generate TAadjustment commands as infrequently as possible to minimize signalingoverhead.

[0013] This is facilitated by using small guard period (GP) with respectto the time slot duration, within each radio frame between transmitteddata of each time slot. A conventional time slot structure is shown inFIG. 3. The GP avoids simultaneous transmission and reception in eitherthe BS or MT. A “physical reception window” of operation, which issubstantially smaller than the GP, dictates the allowed timingdeviation. The physical reception window shifts within the GP as MTpropagation delay changes.

[0014] The measured TD reflects the location of the physical receptionwindow within the GP. The TA provides a corrective shift of the physicalreception window within the GP. It is important to synchronize the TAadjustment in the MT and BS, since the BS reception window shifts aswell. Conventionally, the BS controller continuously monitors the TD foreach MT independently and generates TA commands in advance of theallowed physical reception window being exceeded.

[0015] The logic used to generate TA commands infrequently must alsotake into account the possibility that radio transmission failures cancause TA commands not to be received by the MT. This requires a fast anddeterministic way to recognize when the MT has not performed the TAadjustment.

[0016] The TD and TA can additionally be used to determine the locationof MTs. Since the propagation delay is equatable to the distance betweenan MT and a BS, the TDs from several BSs for a particular MT can be usedto calculate by triangulation the MT location.

[0017] In order to produce accurate TA signals in connection withmaintaining the reception window, minimizing signaling overhead andgeolocation, it is important to know the TA for the time slot the TD wasmeasured. Applicant has recognized that one method to accomplish this isonly to allow the TA to take affect in the MT on specifically identifiedframes.

[0018] The need to coordinate TA adjustment in the MT and TD measurementin the BS to a specific sequential radio frame is difficult since thetime of reception and processing in the MT of the BS generated TAcommand is not known to the BS controller. One conventional method is toonly allow adjustments on periodic frame boundaries. Since the radioframes are sequentially numbered, periodic sequential frame numbers areconventionally used. However, the period needs to be excessively largeto guarantee that the TA command can be processed in advance of the nextperiodic TD measurement.

[0019] To determine the TA frame number period necessary to coordinatethe process, the worst case latency between BS controller generation ofthe TA command to MT processing must be used. This is the minimum periodnecessary to guarantee TA adjustment on the next TA frame number. Forthis case, the BS controller needs to initiate the procedure immediatelyfollowing the previous TA frame number period. This effectively resultsin a TA adjustment delay of up to two TA sequential frame numberperiods.

[0020] As shown in FIG. 4, the worst case latency from BS generation toMT processing of the TA adjustment command is the time between TA framenumbers. The BS may determine a TA command needs to be generated sometime (T1) after TA frame number 1 and a time (T2) before TA frame number2. To guarantee coordination of the time the TA will take effect betweenthe MT and BS, the BS must wait for the previous TA frame number periodto expire to generate the request at time (T3). The result is when theTA requirement is recognized at time T1 the delay to coordinate the TAadjustment is greater than one frame number TA period, and at time T2the delay is less the two frame number TA periods.

(FN TA period)<(actual time to adjust TA)<(2(FN TA period))  Equation 5

[0021] Applicant has recognized that this methodology for TAcoordination using specified frame number TA periods results inexcessive TA delays that can be avoided. For example, excessive delayscan arise due to the potential for failed radio transmissions. In thiscase it is necessary to recognize the failed transmission in the BScontroller as quickly as possible so that a new TA adjustment commandcan be regenerated. Using the frame number TA period method, the BSController will wait for subsequent TD measurements following anexpected TA adjustment to determine if a TA command needs to beregenerated. This case is shown in FIG. 5.

[0022] In this prior art example, the BS controller, after receiving aTD for correction at a time T0, must wait for a subsequent TDmeasurement at time T1 that indicates the TA adjustment did not takeeffect. The difficulty with this signaling method is that the BScontroller does not know exactly which TD measurement identifies the TAadjustment failure. As a result, the BS controller in order to minimizeTA commands must wait for the worst case TA adjustment delay beforeregenerating a TA command base on the received TD measurement.

[0023] Another prior art solution has the MT confirm each TA command asshown in FIG. 6. For this example, a timeout on the TA confirmation willresult in retransmission of the TA command. The TA adjustment failurewill be recognized faster then waiting for the TA frame number period toexpire. However, this faster recovery requires approximately twice asmuch signaling since every command is confirmed. This is undesirable,since a primary objective is to reduce the TA command frequency.

[0024] Accordingly, there exists a need for a system and method thatallows for fast and efficient radio frame timing adjustment withoutexcessive command signaling requirements.

SUMMARY

[0025] The present invention is directed to a system and method forreducing the latency from timing deviation (TD) measurement to timeadvance (TA) adjustment. The invention uses a deterministic procedure tocoordinate time advance (TA) commands and timing deviation (TD)measurements so that failed transmissions or mobile terminals signalpropagation changes can be recognized and corrected much more rapidly.Radio resource efficiency is maximized by minimizing signaling overheadthrough effectively reducing the frequency of time advance commands.This is accomplished by specifying particular radio frames for timeadvance (TA) adjustment by including a Connect Frame Number (CFN) in TAcommands. The potential for timing deviation (TD) measurements to beincorrectly processed is then minimized since the TD measurement made inthe BS for the CFN specified radio frame, in which the TA adjustment wasto be made by the MT, will reflect whether or not the TA was actuallyadjusted.

[0026] A preferred communication system supports base station(BS)/mobile terminal (MT) wireless bi-directional communications via theutilization of a radio frame format having sequentially numbered systemradio frames. System BSs have a transmitter for transmitting selectivelyformatted communication data to MTs within system radio frames and areceiver for receiving communication data from MTs within system radioframes. The BS receivers have an associated processor for measuringtiming deviation (TD) in identified radio frames of communication datareceived from a selected MT.

[0027] Typically, TD measurement is monitored for all radio frames. TheBS processor associates the respective sequential frame number with eachTD measurement of transmissions received in a radio frame therebyestablishing a time associated with each measurement. Timing advance(TA) commands are generated by a base station controller that isassociated with the BSs for providing TA adjustment commands fortransmission by the BSs to the MTs. The TA adjustment command generatorgenerates TA adjustment commands which include the TA adjustment value,calculated based upon the most recent successful TA command's adjustmentand a measured TD for a selected MT. TA adjustment commands also includea Connection Frame Number (CFN) specifying a particular radio frame inwhich the selected MT is to make the timing adjustment.

[0028] It is preferred that the TA signal generator only generates a TAsignal for a selected MT when the measured TD of a transmission receivedfrom the selected MT does not fall within a selected timingsynchronization range, i.e. a TD threshold. Such a TD threshold ispreferably selected to correlate with the physical reception window ofthe MTs and BSs.

[0029] After the BS controller transmits a TA adjustment command to aselected MT, the TD measured for communication data received from theselected MT in the frame specified in the CFN of the transmitted TAcommand signal is analyzed to determine if the TA adjustment has beenmade or if a new TA command is required. Normally, a new TA command willbe immediately required only if the prior TA command did notsuccessfully TA adjust the selected MT. Otherwise the TD measurement forthe CFN frame should be changed by substantially the same amount whichthe TA command was to effect and should fall within the TD threshold.

[0030] Preferred mobile terminals (MTs) have a transmitter and anassociated MT processor for transmitting selectively formattedcommunication data to the BSs within system radio frames synchronized bythe MT processor and a receiver for receiving communication data fromthe BSs within system radio frames. The MT processor adjust the timingof the transmissions of the associated MT transmitter in response to TAdata in a received TA adjustment command commencing in the radio framespecified in the CFN of the received TA command.

[0031] The communication system preferably also includes a geographiclocator associated with the BSs for determining the physical location ofthe MTs. In using conventional triangulation, two or more BSs measuresTDs with respect to communication data received from a selected MT in aspecified system radio frame. However, using the TD measurements aloneto calculate MT geographic location will not produce an accurate resultif the MT signal has been TA adjusted. With the present invention, theTA of the MTs' transmissions are known for virtually all radio frames,since the actual TA is the TA of the most recent TA command signalsuccessfully sent to the MT. Since the TD for each CFN specified radioframe is evaluated, failure of a TA command is known as soon as themeassured TD for the CFN frame is checked which is nearlyinstantaneously. For a successful TA command, its TA value is used ingeolocation calculations for the frame specified by its CFN and allsubsequent frames until a CFN identified frame of the next successful TAcommand. Thus, geographic location calculations may be made with respectto any radio frame based on TA command data which is known to have beeneffectuated.

[0032] The invention also provides a method of synchronizingcommunication data at the BSs. Timing Deviation (TD) is measured inidentified radio frames in which communication data is received from aselected MT by a BS. If the measured TD of a transmission received fromthe selected MT does not fall within a selected timing synchronizationrange, a TA command signal is generated. The TA command signal includesTA data calculated based upon the measured TD. The TA command signalalso includes a Connect Frame Number CFN specifying a particular radioframe for effectuating a timing adjustment by the selected MT. The TAcommand signal is transmitted to the selected MT. If the TA signal isthen received by the selected MT, the timing of the communication datatransmissions of the selected MT is adjusted based on the TA data andcommencing in the CFN specified radio frame of the received TA commandsignal. The TD for data received from the selected MT to which the TAcommand signal had been transmitted is checked for the radio framespecified in the CFN of the transmitted TA command signal to assure theTA command was effected in the selected MT. Preferably, the TA commandsignal generation, transmission and the associated TD checking isrepeated when the TD of a transmission received from the selected MT inthe CFN radio frame does not fall within a selected timingsynchronization range or is not changed by an amount virtually equal tothe TA adjustment, since this would indicate a failure of the selectedMT to implement the previously transmitted TA command.

[0033] The invention also facilitates a method of geographicallylocating a mobile terminal (MT) in a communication system. The methodcomprises effecting MT timing adjustments by communicating timingadvance (TA) command signals to a selected MT, when a measured TD of asignal received by a BS from the selected MT exceeds a TD threshold. TheTA command signals including TA data and a Connect Frame Number CFNspecifying a particular radio frame. Timing Adjustment of communicationdata transmissions by the selected MT are made based on the TA data of aTA command signal in the CFN specified radio frame. The TD forcommunication data received from the selected MT in the CFN specifiedradio frame of a TA command signal is checked to determine whether therespective TA command signal was successfully effected by the selectedMT, thereby assuring the actual TA of the selected MT is known. Measuredtiming deviation (TD) of a transmission received for a selected radioframe from a selected MT one or more BSs is collected. The TA data ofthe most recent successful TA command signal and the TD measurements bythe BSs for the selected radio frame are used to calculate thegeographic location of the selected MT.

[0034] Other objects and advantages of the system and method will becomeapparent to those skilled in the art after reading the detaileddescription of the invention.

BRIEF DESCRIPTION OF THE DRAWING(S)

[0035]FIG. 1a is a schematic timing diagram of radio frame reception andtransmission at a mobile terminal without any timing adjustment.

[0036]FIG. 1b is a schematic timing diagram of radio frame reception andtransmission at a base station without any timing adjustment.

[0037]FIG. 2a is a schematic timing diagram of radio frame reception andtransmission at a mobile terminal with timing advance.

[0038]FIG. 2b is a schematic timing diagram of radio frame reception andtransmission at a base station with a timing advance adjustment.

[0039]FIG. 3 is an illustration of a conventional time slot data andguard period structure.

[0040]FIG. 4 is a timing diagram of a conventional time adjustmentmethod based on periodic frame number.

[0041]FIG. 5 is a timing diagram of timing adjustment command failureand retransmission under the conventional method illustrated in FIG. 4.

[0042]FIG. 6 is a timing diagram of an alternative conventional methodof timing adjustment utilizing command confirmation signaling.

[0043]FIG. 7 is a timing diagram of frame number synchronized time delaymeasurement and timing adjustment in accordance with the teachings ofthe present invention.

[0044]FIG. 8 is a timing diagram of recovery from failed timingadjustment in accordance with the teachings of the present invention

[0045]FIG. 9 is a schematic diagram of a communicating system made inaccordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0046] The embodiments will be described with reference to the drawingfigures where like numerals represent like elements throughout.

[0047] Referring to FIG. 9, there is illustrated a communication system10 comprising a plurality of base stations (BSs) 12 which conductwireless communication with mobile terminals (MTs) 14. Each BS conductswireless communications with MTs in a geographic cell, which cell areasnormally have some overlap. Where an MT 14 is in an overlap area,bi-directional communication is generally conducted by the BS having thestrongest signal link with the MT. Where a second BS begins to have astronger signal link, “hand off” of the communication occurs. Desiredparameters and procedures for effectuating “hand off” are well known inthe art.

[0048] In a preferred system such as in accordance with 3G wirelessprotocols, node Bs 16 are provided in a physical or logical connectionwith the one or more BSs. A radio network controller (RNC)17, to whichthe node Bs 16 are connected, controls the BSs and coordinatescommunications over the communication system 10. Multiple RNC's 17coordinate communications for different BS groups in an extended system.The RNC 17 includes a BS controller which controls the BSs within thenode Bs. Preferably the RNC 17 includes an MT geographic locator, but itis not required that the geographic locator be implemented in the RNC17.

[0049] Each BS 12 preferably includes a transceiver 20 with anassociated antenna system 22 and BS signal processing circuitry 24. EachMT 14 preferably includes a transceiver 26 with an associated antenna 27and MT signal processing circuitry 28. In lieu of transceivers, BS andMT transmitters and receivers may be embodied as separate components.

[0050] Downlink communications (DL) are processed by the BS processingcircuitry 24 and transmitted via the BS transceivers 20 from the BSantenna systems 22 for reception by the MTs 14. Uplink communications(UL) are transmitted from the MTs 14 and received via the BS antennasystems 22 and BS transceivers 20 of the base stations 12.

[0051] The BS processing circuitry 24 implements the formatting ofwireless BS/MT communications into a selected radio frame format havingmultiple time slots, which format is used on a system wide basis for allBSs controlled by the RNC 17. Preferably, the RNC and node Bs coordinatethis implementation.

[0052] Within the radio frame format, each radio frame is assigned asequential number which enables the processing circuitry to identifyspecific system frames in the wireless BS/MT communications. The BScircuitry 24 is configured to measure received time delays (TDs) suchthat each TD measurement is identified with the respective radio frameof a received MT transmissions, i.e. uplink communications. Thesequential frame numbers of the radio frames are used for this purpose.

[0053] The BSs provide TD data to the BS controller of the RNC 17 whichpreferably includes TD measurement data recorded at the BSs,identification of the MT which made the measured UL transmission and thesystem radio frame number in which the measured UL transmission wasreceived. When the TD measurement data exceeds a specified threshold,the BS controller generates a TA command for the respective MT. Aconventional intelligent algorithm is used to determine direction andspeed of the MT with respect the measuring BS based upon TD measurement.

[0054] Preferably, the communication time slots have a guard period of apredetermined length within which a physical reception window moves. TheTD threshold is preferably slightly shorter than the physical receptionwindow and takes into account failed adjustments and time to detectfailure and retry adjustment.

[0055] An initial TD measurement TD₀ reflects the initial position ofthe physical reception window within the GP for a particular MT beforeany TA adjustment. An initial TA, TA₀, is made at the MT which, assumingTA₀ is successful, relocates the physical reception window to a desiredlocation reflected by a new timing deviation measurement TD₁. Theinitial TA, TA₀, was successful if TD₁+TA₀ is virtually equal to TD₀.

[0056] The TA of the MT transmission remains constant until the nextsuccessful TA adjustment as reflected by the measured TD. For example,an initial successful command TA₀ could set the frame advance of the MTtransmission to 8 units, a next TA command TA₁ could command the advancethe MT transmission to be changed to 3 units. The success of TA₁ wouldbe reflected in a retardation of the measured TD of a received MTtransmission of 5 units. If TA₁ was not successfully implemented, the TAof the MT transmissions would remain at 8 units.

[0057] To establish the time when TA adjustments take place, TA commandsaccording to the invention specify a particular radio frame when the TAadjustment is to be made by the MT. Thus, each TA command signalincludes TA data and a Connect Frame Number (CFN) which specifies aparticular radio frame in which the MT will effectuate a TA command.

[0058] Upon determining TA adjustment is necessary, the BS controllergenerates a TA command signal without incurring the delay required forthe prior art periodic TA frame number based adjustment method such asdiscussed in connection with prior art FIG. 4. Each TA command sent tothe MT indicates a specific frame identified by the CFN when the MT willperform the TA adjustment. As illustrated in the signaling flow diagramshown in FIG. 7, when the BS controller determines TA adjustment isnecessary, based on received TD measurements at time T1, a TA command isimmediately generated. Only an extremely short BS controller processingdelay is incurred so time Ti is approximately equal to time T2. The TAcommand includes a CFN specifying the particular radio frame at a timeT3, when the MT performs the TA as illustrated in FIG. 7. The CFN isselected so that TA adjustment is applied at a time accounting for theexpected BS controller to MT propagation and MT processing delay andthat the CFN identified frame as transmitted by the MT will arrive atthe BS with a corrected TD.

[0059] Since the BS controller specified the frame number in which theTA adjustment was to occur, a TD measurement at T4 conducted by the BSfor the CFN specified time slot as received at the BS indicates to theBS controller if the TA was successfully performed by the MT. If TD ofthe CFN frame received at the BS is changed by substantially theadjustment to the timing which was to be effected by the TA commandsignal, the TA command was successful. If not, the BS controller canvery quickly react to failed TA command transmissions and, also, can actto readjust MTs that have considerably changed distance from the BSsince time Ti by issuing a new TA command signal.

[0060] The case of a failed TA adjustment command is shown in FIG. 8.The TA command has not been processed by the MT, so that a TA adjustedsignal is not transmitted in the CFN frame at T0 by the MT. The TDmeasurement at the BS at time T1 on the CFN frame specified in the TAcommand, accordingly, does not indicate the TA adjustment has takenplace. The base station controller then generates a new TA command attime T2. Since a deterministic method has been used to synchronize TAadjustment to a known frame number by the MT and BS controller, verylittle time is needed to generate the new TA command signal. Thus, timeT2 is approximately equal to time T1.

[0061] The ability for the BS controller to react immediately uponreception of the TD measurement on the frame number specified in theprevious TA command allows more time to generate TA commands withoutexceeding the physical channel reception window or overwriting theneighboring time slot guard period. This results in lowering therequired frequency of TA commands and correspondingly reduces thephysical resources required to support the TA signaling function.

[0062] The invention additionally allows for the case of a MT that haschanged distance with respect to the BS to be quickly distinguished fromthe failed TA command case. Since the BS controller specifies via theCFN the particular radio frame a TA is to take effect, the TDmeasurement received for that particular radio frame will indicate ifthe TA command was correctly received and performed by the MT.Accordingly, TD measurements outside the specified threshold occurringin the CFN specified time frames will normally indicate failed TAcommands, while such TD measurements in other time frames will normallyindicate a change in MT location. Even where the TD measurement of areceived CFN specified time frame is attributable to MT relocation, thenew TA signal is generated based on that TD measurement to produce anaccurate TA for the MT. This is an important capability since the BScontroller is aware of is a previously failed TA command adjustment sothat a complete adjustment can be made avoiding the need to repeat thefailed TA command.

[0063] For geolocation, the geolocator can employ triangulation ofreceived signals from a selected MT by several BSs with a higher degreeof reliability. Where a selected MT is in communication with a BS forconducting normal telecommunications, that BS normally transmits the TAcommand signals generated by the BS controller to the selected MT. Sincein accordance with the invention, the TA of MT transmissions is knownfor all radio frames, the geographic location can be easily calculatedby conventional triangulation methods utilizing the known location ofthe BS, the TA data of most recent successful TA command signal (or 0where no TA commands have been successful), and TD measurements from oneor more BSs. While it is possible to provide geographic location basedusing triangulation upon the TA, the TD measurements from two BSs,unambiguous geographic location information via conventionaltriangulation is provided where TD measurements are obtained from atleast three BSs.

[0064] In TDD systems where there is only communication with one BS, theMT also measures relative frame reception difference between cells. Thecell reception difference measurements combined with distance from thecurrent cell as reflected by the TD measured at the BS allows forgeographic location determination in such systems based on the TA of theMT and the single BS TD measurement. It is also known to use pathlossmeasurements in such calculations.

[0065] Preferably, when a geographic location request is received, thegeographic locator specifies a system time frame in which BS TDmeasurement of received transmissions from the selected MT is collectedfrom the BS in primary communication with the selected MT, in a TDDsystem, and, in a conventional BS triangulation system, also from one ormore other BSs. The geolocation is calculated based upon the TDmeasurements gathered for the specified time frame and the TA reflectedby the most recent successful TA command effected by the selected MT.Accordingly, accurate geographic location of MTs can be performedvirtually at all times since the TA of the selected MT is known from theTA command signals which have been successful as determined inaccordance with this invention.

[0066] While the present invention has been described in terms of thepreferred embodiments, other variations which are within the scope ofthe invention as outlined in the claims below will be apparent to thoseskilled in the art.

What is claimed is:
 1. A communication system for supporting basestation (BS)/mobile terminal (MT) wireless bi-directional communicationsvia the utilization of a radio frame format having sequentiallyidentified system radio frames comprising: a BS having: a transmitterfor transmitting selectively formatted communication data to MTs withinsystem radio frames, and a receiver for receiving communication datafrom MTs within system radio frames; said BS receiver having anassociated processor for measuring timing deviation (TD) of received MTtransmissions in identified radio frames in which communication data isreceived from a selected MT; a timing advance (TA) signal generatorassociated with said BS for providing TA command signals fortransmission by said BS to selected MTs; said TA command signalgenerator generates TA command signals which include: TA data which iscalculated based upon measured TD in an identified radio frame for aselected MT, and a Connect Frame Number (CFN) specifying a particularradio frame for effectuating a timing adjustment by the selected MT; andsaid BS processor measuring the TD for communication data received froma selected MT to which a TA command signal had been transmitted in theframe specified in the CFN of the transmitted TA command signal.
 2. Acommunication system according to claim 1 wherein: said TA commandsignal generator only generates a TA command signal for a selected MTwhen a measured TD of a transmission received from the selected MT doesnot fall within a selected timing synchronization range.
 3. Acommunication system according to claim 1 further comprising: at leastone mobile terminal (MT) having: a transmitter and an associated MTprocessor for transmitting selectively formatted communication data to aBS within system radio frames synchronized by said MT processor; and areceiver for receiving communication data from a BS within system radioframes; and said MT processor adjusting the timing of the communicationdate transmitted by said MT transmitter in response to TA data in areceived TA command signal commencing in the radio frame specified inthe CFN of the received TA command signal.
 4. A communication systemaccording to claim 3 wherein: said TA signal generator only generates aTA signal for a selected MT when the identified TD of a transmissionreceived from the selected MT does not fall within a selected timingsynchronization range.
 5. A communication system according to claim 1further comprising: a plurality of base stations (BSs), each having: atransmitter for transmitting selectively formatted communication data toMTs within system radio frames, and a receiver for receivingcommunication data from MTs within system radio frames; each said BSreceiver having an associated processor for measuring a timing deviation(TD) of received MT transmissions in identified radio frames in whichcommunication data is received from selected MTs; said timing advance(TA) command signal generator associated with each said BS for providingeach said BS selected TA command signals for transmission to respectiveselected MTs; and each said BS processor measuring the TD forcommunication data received from a respective selected MT to which arespective TA command signal had been transmitted in the frame specifiedin the CFN of the respective transmitted TA command signal.
 6. Acommunication system according to claim 5 wherein: said TA commandsignal generator only generates a TA command signal for a selected MTwhen the measured TD of a transmission received from the selected MTdoes not fall within a selected timing synchronization range.
 7. Acommunication system according to claim 5 further comprising: ageographic locator associated with said BS controller and said BSs suchthat measured TD by one or more of said BS processors with respect tocommunication data received from a selected MT in a specified time frameprovides a basis for calculating the geographic location of the selectedMT during the specified time frame in conjunction with the TA data of amost recent successful TA command signal issued by the BS controller tothe selected MT.
 8. A communication system according to claim 5 furthercomprising: a plurality of mobile terminals (MTs), each having: atransmitter and an associated processor for transmitting selectivelyformatted communication data to said BSs within system radio framessynchronized by said processor; and a receiver for receivingcommunication data from said BSs within system radio frames; and eachsaid MT processor adjusting the timing of communication data transmittedby said respective MT transmitter in response to TA data in a receivedTA command signal commencing in the time frame specified in the CFN ofthe received TA command signal.
 9. A communication system according toclaim 3 wherein: said TA command signal generator only generates a TAcommand signal for a selected MT when the measured TD of a transmissionreceived from the selected MT does not fall within a selected timingsynchronization range.
 10. A mobile terminal (MT) for a communicationsystem which supports base station (BS)/mobile terminal (MT) wirelessbi-directional communications via the utilization of a radio frameformat having sequentially identified system radio frames where a BStransmits selectively formatted communication data to MTs within systemradio frames, including timing advance (TA) command signals whichinclude TA data and a Connect Frame Number (CFN) specifying a particularradio frame for effectuating a timing adjustment by a MT, the mobileterminal (MT) comprising: a transmitter and an associated processor fortransmitting selectively formatted communication data to a BS withinsystem radio frames synchronized by said processor; and a receiver forreceiving communication data from the BS within system radio frames; andsaid MT processor adjusting the timing of communication data transmittedby said MT processor in response to TA data in a received TA commandsignal commencing in the radio frame specified in the CFN of thereceived TA command signal.
 11. A method of synchronizing communicationdata at a base station for a communication system supporting wirelessbi-directional communications between a base station (BS) and aplurality of mobile terminals (MTs) via the utilization of a sequentialradio frame format having identified system radio frames, where the BStransmits selectively formatted communication data to MTs within systemradio frames and receives communication data from MTs within systemradio frames, and at least one mobile terminal (MT) transmitsselectively formatted communications data to the BS within system radioframes and receives communication data from said BS within system radioframes, the method comprising: a) measuring timing deviation (TD) ofcommunication data received from a selected MT by the BS and performingthe following steps when the measured TD does not fall within a selectedtiming synchronization range; b) generating a TA command signal whichincludes: TA data calculated based upon the measured TD of thecommunication data received from the selected MT, and a Connect FrameNumber (CFN) specifying a particular radio frame for effectuating atiming adjustment by the selected MT; c) transmitting the TA commandsignal to the selected MT; d) if the TA command signal is received bythe selected MT, adjusting the timing of communication data transmittedby the selected MT in response to the TA command signal based on the TAdata and commencing in the radio frame specified by the CFN of thereceived TA command signal; and e) measuring the TD for communicationdata received from the selected MT in the radio frame specified by theCFN of the transmitted TA command signal.
 12. The method of claim 11further comprising: repeating steps b)-e) when the measured TD of atransmission received from the selected MT in step e) does not fallwithin the selected timing synchronization range.
 13. The method ofclaim 12 wherein steps b)-e) are performed whenever measured TD ofcommunication data received from the selected MT does not fall withinthe selected timing synchronization range.
 14. A method ofgeographically locating a mobile terminal (MT) in a communication systemhaving a plurality of base stations (BSs) supporting wirelessbi-directional BS/MT communications via the utilization of a sequentialradio frame format having identified system radio frames where the BSstransmit selectively formatted communication data to MTs within systemradio frames and receive communication data from MTs within system radioframes and where the MTs transmit selectively formatted communicationsdata to the BSs within system radio frames and receive communicationdata from said BSs within system radio frames, the method comprising:communicating timing advance (TA) command signals to a selected MT whichsignals include TA data and a Connect Frame Number (CFN) specifying aparticular radio frame for effectuating a timing adjustment by theselected MT; measuring timing deviation (TD) in each CFN specified radioframe of communication data received from the selected MT by a BS todetermine whether each respective command signal was successful;measuring timing deviation (TD) of a received MT transmission from theselected MT in a selected radio frame by said BS; and using the measuredTD from the selected radio frame and the TA data of a most recentsuccessful TA command signal transmitted to the selected MT to calculatethe geographic location of the selected MT.
 15. The method according toclaim 14 wherein timing deviation (TD) of communication data receivedfor the selected MT by a second BS in the selected radio frame ismeasured and also used in the calculation of geographic location of theselected MT.
 16. The method according to claim 15 wherein timingdeviation (TD) of communication data received for the selected MT by asecond BS in the selected radio frame is measured and also used in thecalculation of geographic location of the selected MT.
 17. The methodaccording to claim 14 wherein the selected MT measures relative framereception difference between cells and the cell reception differencemeasurements are also used in calculating geographic location.